Similar to rare metals like lanthanum, there are many that are extremely scarce on Earth.
Some rare metals aren't needed by Jiang Cheng now, but sooner or later there will come a day when they are needed.
There are some special materials of which not even a bit exists on Earth.
Such as the Alpha Crystal, which is a necessary material for manufacturing mechas, not a trace can be found on Earth.
But if one day Alpha Crystals won't suffice, Jiang Cheng will have to go look on Neptune.
It can be said that the rare minerals available on Earth simply cannot support his future plans, nor can they allow humanity to develop into a space civilization.
Yet Jiang Cheng believes that humanity is destined to become a space civilization in the future, a goal he has already set for humanity.
So after Jiang Cheng discovered this fact, he decided to vigorously exploit resources elsewhere.
